This invention relates to an improved form of composite golf shaft. In particular, this invention is concerned with a golf shaft having a tubular metallic core having graphite fiber reinforcing layers superimposed thereon.
There are numerous factors which affect the performance characteristics of golf shafts such as weight and balance of the shaft, the flexibility of the shaft and the ability of the shaft to withstand shock. Additionally, of course, a golf shaft of optimum design must maintain its performance characteristics over a wide range of ambient weather conditions, and it should be resistant to moisture and other corrosive elements such as hand perspiration and the like.
In addition to the foregoing considerations, it is well known that there is a somewhat intangible, but nonetheless real and important, characteristic of a golf shaft referred to as the "feel" which has a very definite effect on the playability of the shaft as well as the commercial acceptance of the shaft.
A considerable amount of effort has been expended in the past to produce golf club shafts having the desired performance characteristics. Thus, golf club shafts have been made from wood, such as hickory, and metals, such as steel and aluminum. The wooden shafts have the advantage of not transferring vibrational shocks to the player when the ball is struck during play. On the other hand, the wooden shafts suffer from the disadvantage that they are not easily matched into a complete set. They are very much subject to changes in climatic weather conditions. Metal shafts generally are not susceptible to variations in physical characteristics and response to climatic changes; however, tubular metal golf shafts transfer a great amount of vibration to the player when the club head strikes the golf ball. Attempts have been made to remedy the deficiencies of the tubular golf shafts by coating the metal tube with a resin-impregnated glass fiber. Use of such resin-impregnated glass fiber coatings on tubular shafts, however, has the tendency to provide a dampening effect on the vibrations normally experienced. Nonetheless, such coatings have introduced other changes in the playing characteristics of the club. Indeed, one of the particular difficulties associated with fiber reinforced resin coatings on tubular metal shafts is associated with the significant difference in the physical properties of the two essential materials, i.e. the metal and the glass fiber. To get the requisite performance from the golf shaft, both materials must be combined in such a way as to operate harmoniously in producing the desired result. This has not been readily achieved in the past. Moreover, glass fiber reinforced metal tubes tend to require increased weight to maintain the requisite torsional and bending stiffness. Finally, it is worth noting that durability tends to be a problem when bonding dissimilar materials. Consequently, there still remains need for an improved golf shaft that will have the necessary strength and weight and which will permit the player to attain greater hitting force and control and which can be accurately adjusted to provide a set of matched golf clubs each having the same "feel".